The present application generally relates to emissions testing of powertrain systems including a diesel engine and a motor/generator, and unique configurations and operation of such systems meeting or exceeding state of the art performance and emissions criteria.
Diesel engines present unique challenges relative to emissions including a need to simultaneously limit emissions to the environment of so-called criteria emissions including NOx, particulates, hydrocarbons, and CO, as well as limit other emissions including CO2 while also meeting performance requirements. Emissions standards typically require engine output to meet a defined schedule of output shaft torque and speed requirements which simulate a broad range of operating conditions encountered in real world operation.
The United States currently requires heavy duty diesel engines to operate according to the transient FTP duty cycle or steady state SET duty cycle with emissions not exceeding 0.20 grams of NOx per brake horsepower-hour, 0.01 grams of particulate matter per brake horsepower-hour, 0.14 grams of Non-Methane Hydrocarbons (NMHC) per brake horsepower-hour, 15.5 grams of CO per brake horsepower-hour. Details of the FTP and SET duty cycles are known to those of skill in the art and are set forth in 40 CFR 86.007-11, 40 CFR 1065, and 40 CFR 86.1360-2007. Similarly, Europe currently requires heavy duty diesel engines to operate according to the Euro VI standards which require emissions not exceeding 0.40 grams of NOx per brake kilowatt-hour, 0.01 grams of particulate matter per brake kilowatt-hour, 0.13 grams of hydrocarbons per brake kilowatt-hour, 1.5 grams of CO per brake kilowatt-hour. Additionally, CO2 emissions criteria for heavy duty diesel engines are being established. Current proposals are to limit CO2 emissions to less than 500 grams per brake horsepower hour over a test cycle including transients.
To meet competing state of the art emissions and performance requirements, existing systems rely upon combinations of exhaust gas recirculation (“EGR”), variable geometry turbochargers (“VGT”), selective catalytic reduction (“SCR”), and diesel particulate filtration (“DPF”). Reliance on these features has been widely accepted and adopted; so much so that the only engines currently certified to meet the aforementioned emissions requirements rely upon EGR, VGT, SCR, and DPF. While successful, these features impose complexity, cost, and fuel economy penalties as a trade off for emissions control. Some proposed diesel systems rely upon homogeneous combustion modes such as homogeneous charge compression ignition (“HCCI”), homogeneous charge late injection (“HCLI”), other homogeneous combustion modes to reduce emissions, typically in combination with EGR, SCR, DPF, VGT or other techniques. While providing certain emissions benefits over non-homogeneous combustion diesel engines, homogeneous combustion diesel engines pose notoriously difficult control problems and impose significant cost and complexity.